Five inches of super insulated shell are installed around the exterior of the buildings. Along with an insulated roof, high-efficiency windows and extensive air sealing systems, these components improved the effectiveness of the insulation by a factor of ten, while also improving air quality.

Additional energy savings have been achieved with high-efficiency cooling and heating equipment, LED and CFL lights, Energy Star appliances and solar hot water systems.

The designers say the key difference between a standard retrofit and a deep energy retrofit is this super insulation.

The two photos below show the building before and after the insulation wrap.

After:

Before the renovation, gas for heating and hot water cost building owners $194,000 a year; that's been slashed to $50,000. Electric bills, which are paid by residents, are cut in half, from $397,000 annually to $181,000, according to the Castle Square Tenants Organization.

"Given the potential benefits of deep energy retrofits, should incentivizing them become part of public policy? We hope so. Other clean energy sources are supported by national public policy, such as federal renewable energy tax credits, and deep energy retrofits could be as well. As a matter of fact, deep energy retrofits currently perform better than small-scale solar on a dollar per dollar basis.

"For example, at Castle Square, if we installed the equivalent number of solar panels to produce as much energy as was saved through the deep energy retrofit, the cost would have been approximately $35,759 per apartment (compared with the incremental cost of $18,023 per apartment for the deep energy retrofit). In the case of Castle Square, the deep energy retrofit (governmental incentives not withstanding) was more economically rational than the equivalent solar PV system."

The renovation completed by WinnDevelopment was funded through several incentive programs, including the Department of Housing and Urban and Development and the Massachusetts Department of Energy Resources.